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Agilent
PNA Microwave Network Analyzers
Application Note 1408-11
Accurate Pulsed Measurements
High Performance Pulsed S-parameter Measurements
Vector network analyzers are traditionally used to measure the continuous wave (CW)
S-parameter performance of components. Often under these operating conditions the
analyzer is functioning as a narrowband measurement instrument. It transmits a known
CW frequency to the component and measures the CW frequency response. If we were
to look at the response of a single CW frequency we would see a single spectral tone in
the frequency domain. The analyzer has a built in source and receivers that are designed
to operate together in a synchronous manner, utilizing narrowband detection, to measure
the frequency response of the component. Most analyzers can be configured to generate
a frequency sweep over many frequency tones.
In some cases the signal applied to the component must be pulsed (turned on and off)
at a specific rate and duration. If we were to look at the frequency domain response of
a single pulsed tone, it would contain an infinite number of spectral tones making it
challenging to utilize a standard narrowband VNA. This article describes how to configure
and make accurate pulsed S-parameter measurements using the Agilent microwave
PNA network analyzer.
Pulsed Signals
To see what the frequency domain spectrum of a pulsed signal looks like we first
mathematically analyze the time domain response. Equation 1 illustrates the time domain
relationship of a pulsed signal. This is generated by first creating a rectangular windowed
version (rect(t)) of the signal with pulse width PW. A shah function is then realized
consisting of a periodic train of impulses spaced 1/PRF apart where PRF is the pulse
repetition frequency. This can also be viewed as impulses at spacing equal to the pulse
period. The windowed version of the signal is then convolved with the shah function to
generate a periodic pulse train in time corresponding to the pulsed signal.
1 (t)
y(t) = (rectpw(t)